1. Field of the Invention
This invention relates to a two-wheel and four-wheel driving change-over device for a vehicle.
2. Description of Background Art
A vehicle is known in the prior art wherein the operating condition can be changed over between two-wheel drive and four-wheel drive.
FIGS. 4 and 5 illustrate one example of the aforesaid vehicle. In FIGS. 4 and 5, the vehicle 1 includes a vehicle body frame 3 having an engine 2 mounted at a central part thereof. Front wheels 4 and rear wheels 5 are mounted at both the front and rear sides of the vehicle body frame 3. A steering handlebar 6 is positioned at the forward upper part of the vehicle body frame 3 for steering the front wheels 4. A fuel tank 7 is fixed above the engine 2 and is mounted on the vehicle body frame 3. A seat 8 is fixed to the rear part of the fuel tank 7.
As shown in FIG. 5, each of the front wheels 4 is supported by suspension devices 9 installed at both of the front sides of the vehicle body frame 3 in such a way that the front wheels may be moved up and down. Each of the rear wheels 5 is supported by suspension devices 10 installed at both of the rear sides of the vehicle body frame 3 in such a way that the rear wheels may be moved up and down.
In addition, a forward central part and a rearward central part of the vehicle body frame 3 are provided with a final gear reducer 13 for front wheels and a final gear reducer 14 for rear wheels connected to the engine 2 by propeller shafts 11, 12, and the right and left front wheels 4 and the right and left rear wheels 5 are connected to each of these final gear reducer 13 for the front wheels and final gear reducer 14 for the rear wheels.
Then, for example, between the final gear reducer 13 for the front wheels and the propeller shaft 11 is arranged a two-wheel and four-wheel driving change-over device for connecting or disconnecting power transmitted to the front wheels 4 and changing over between the rear wheel drive and the four wheel drive.
In some cases, the two-wheel and four-wheel drive change-over device is arranged between the rear propeller shaft 12 and the final gear reducer 14 for the rear wheels for changing over between the front wheel drive and the four-wheel drive.
This change-over of the driving states is dependent on a road surface state and a running form and this is changed over by a driver when required.
For the two-wheel and the four-wheel change-over device, the structure shown in FIG. 6, for example, has been proposed.
In FIG. 6, the two-wheel and four-wheel driving change-over device denoted by reference numeral 15 is constituted of two input shaft composing units 16a and 16b in which an input shaft 16 for the final gear reducer 13 for the front wheels is formed to be axially divided into two segments and abutted to each other on the same axis, and a change-over unit 17 is provided for performing connecting and disconnecting operations of these units.
Describing it in detail, a column-like position setting protrusion 18 protrudes at a central part of the end surface of the input shaft composing unit 16a positioned at the final gear reducer 13 for the front wheels. In addition, the central part of the end surface of the input shaft composing unit 16b positioned outside is formed with a position setting recess 19 to which the position setting protrusion 18 is rotatably fitted. Both input shaft composing units 16a and 16b are abutted to each other in such a way that the position setting protrusion 18 and the position setting recess 19 are fitted to each other, thereby both input shaft composing units 16a, 16b are positioned on the same axis and they are connected in a relative rotatable manner.
In addition, an outer circumferential surface of the abutting part of each of both input shaft composing units 16a and 16b is formed with a spline (not shown) and a change-over unit 17 so as to enclose the abutted part.
The change-over unit 17 is constituted of a change-over ring 20 formed with a spline at its inner surface, slidably fitted to the abutting part of both input shaft composing units 16a, 16b and engaged with or disengaged from each of the splines. A driving mechanism 21 is composed of a solenoid for selectively moving the change-over ring 20 to a position where the change-over ring is slid in an axial direction of both input shaft composing units 16a, 16b and engaged only with one input shaft composing unit 16a and a position where the change-over ring is concurrently engaged with the splines of both input shaft composing units 16a, 16b. 
The two-wheel and four-wheel driving change-over device 15 provides a two-wheel driving state in which the change-over ring 20 is moved in one direction by the driving mechanism 21, engaged only with the input shaft composing unit 16a to shut off transmission of the driving force toward the front wheels 4 and only the rear wheels are driven, and a four-wheel driving state in which the change-over ring 20 is slid, the change-over ring 20 is engaged with the input shaft composing unit 16b under a state in which the change-over ring 20 is engaged with the input shaft composing unit 16a, thereby both input shaft composing units 16a and 16b are connected to each other, the driving force is transmitted to the front wheels 4 and then both front wheels 4 and rear wheels 5 are concurrently driven.
However, such a two-wheel and four-wheel driving change-over device 15 of the prior art leaves some problems to be improved as follows.
When the driving form is changed over, if there is a slight difference in peripheral speed between the front wheels 4 and the rear wheels 5, a problem results in that an engagement between the change-over ring 20 and the input shaft composing unit 16b is not performed well and the change-over cannot be carried out.
Further, even in the case where the change-over is performed, there is also a problem that the splines abut to each other when the change-over is performed and an unusual noise is produced.
Then, in order to solve such problems as above, it becomes necessary to provide a mechanism in which the spline in the change-over ring 20 and the spline in the input shaft composing unit 16b are synchronized to each other (their positions are aligned to each other), so that the structure becomes complex, and when the two-wheel and four-wheel driving change-over device 15 is assembled, it is necessary to substantially change the members at the assembled positions from the existing structure.
The present invention provides a two-wheel and four-wheel driving change-over device for a vehicle in which its constitution is simple, assembling can be carried out with as few changes in the existing construction as possible and less frequent occurrences of unusual noise.
A two-wheel and four-wheel driving change-over device for a vehicle described in a first aspect of the present invention is made such that there is provided a change-over unit arranged either at a power transmission mechanism installed between an engine and the front wheels or at a power transmission mechanism installed between the engine and the rear wheels and for performing intermittently power transmission at this power transmission mechanism characterized in that this change-over unit is constituted of a driving shaft connected to a driving side. A driven shaft is fitted to the driving shaft with an annular clearance being provided. A plurality of engaging or disengaging members are installed at a clearance between the driving shaft and driven shaft. The plurality of engaging or disengaging members are engaged with or disengaged from these opposing surfaces to perform a connecting operation and a disconnecting operation between the driving shaft and driven shaft. A change-over mechanism is provided for selectively positioning the engaging or disengaging members between a position where the driving shaft and driven shaft are connected and a position where said driving shaft and driven shaft are disconnected. A casing encloses the above components.
A two-wheel and four-wheel driving change-over device for a vehicle according to a second aspect of the present invention includes a power transmission mechanism having the change-over unit according to the first aspect installed therein is provided with a final gear reducing unit, the driven shaft is inserted into this final gear reducing unit as an input shaft of the final gear reducing unit, a casing for the change-over unit is fixed to the final gear reducing unit and the casing is provided with bearings for supporting the driving shaft and driven shaft.
A two-wheel and four-wheel driving change-over device for a vehicle according to a third aspect of the present invention includes an outer ring to which either the driving shaft or driven shaft is connected through a spline that is rotatably installed in the casing according to the first or second aspect. An inner ring is provided to which either the driven shaft or the driving shaft is connected through a spline that is internally inserted in this outer ring in a coaxial manner, and the engaging or disengaging member is installed between the outer ring and inner ring.
A two-wheel and four-wheel driving change-over device for a vehicle according to a fourth aspect includes the change-over mechanism according to any one of the first to third aspect for disengaging the driven shaft from the driving shaft when the vehicle is braked.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.